Preparation of organic derivatives of cellulose



Patented Nov. 29, 1938 UNITED STATES PREPARATION OF ORGANIC DERIVATIVESF CELLULOSE Camille Dreyfus, New York, N. Y., and George Schneider,Montclair, N. J., assignors to Gelanese Corporation of America, acorporation of Delaware No Drawing. Application November 21, 1935,Serial No. 50,872

Claims. (Cl. 260-230) This invention relates to the treatment of organic derivatives of cellulose to remove therefrom compounds which causesolutions of the organic derivatives of cellulose to corrode metal 5parts with which they come into contact and to remove therefromcompounds which cause haze and cloudy, spots in sheets, films andarticles made from such organic derivatives of cellulose.

An object of this invention is the economic production of organicderivatives of cellulose which, when dissolved in a liquid solvent, haveno corrosive action on metals with which they contact. Another object ofthe invention is the economic production of a highly transparent organicderivative of cellulose product which is free from haze or cloudy spots.A still further object of this invention is the production of filamentswhich are uniform in physical characteristics .throughout their length.Other objects of the invention will appear from the following detaileddescription.

Organic derivatives of cellulose, such as cellulose acetate, asordinarily made contain certain colored constituents or ingredients thattend to impair the usefulness of such derivatives of cellulose in themaking of plastics, films, filaments and the like, particularly wheretransparency and freedom from color are desired. Thus, a thick sheet orblock made of a plastic composition containing such derivatives ofcellulose has a distinct greenish brown color and is of poortransparency.

Furthermore, such derivatives of cellulose also contain certainconstituents or ingredients that 35 tend to corrode metal machineelements and parts of filament-spinning and block pressing devices. Forinstance, in spinning a solution of cellulose acetate dissolved in avolatile solvent by extruding the same through suitable orifices 40 intoan evaporative or precipitating medium, the

spinning solutions containing cellulose acetate as normally made-tend tocorrode the jet holes or orifices. If the corroded material remains inthe jet hole, there is produced a filament hav- 45 ing a denier belowthat desired, while if the corroded material is broken away from the jethole, the jet hole is enlarged and results in a filament having agreater denier than that desired and of undesirable cross-section. Ithas been the practice heretofore to frequently change the spinning jetsand to make periodic examination as to their condition. These operationsnecessarily interrupt the spinning. Moreover, jet replacements arecostly. Furthermore, if improper inspection is made or the jets are notreplaced frequently, there is produced a yarn which is not uniform as todenier, cross-section, etc. This non-uniformity of the yarn reflects inthe fabric produced from the same, producing a fabric of inferiorquality.

Solutions of organic derivatives of cellulose normally have presenttherein compounds which vary in type and chemical nature and whichexhibit different corrosive effects. Thus, one type of corrosive effectis manifested when acetone solutions of cellulose acetate are brought incontact with mercury, resulting in a. rapid blackening of the mercury. Asecond type of corrosive effect is shown by the formation of a brownslimy material which collects about a copper specimen when immersed inthe solution containing the organic derivatives of cellulose. terial maybe readilydissolved in or dispersed through the solution when it isagitated. A third type of corrosive effect is shown by the production ofa green growth about a copper This slimy Ina-- specimen after four orfive days standing in the solution of organic derivatives of cellulose.The

fourth type of corrosive effect is shown by the from solutions oforganic derivatives of celluloser 'by treating the same with metals. Bytreating a solution of the organic derivatives of cellulose with metals,the corrosive constituents are either destroyed or are converted intocompounds that may be removed by filtering or they may be converted intocompounds that tend to reduce such objectionable action to asubstantially unappreciable amount.

In accordance with our invention, we prepare derivatives of cellulose ofreduced corrosive properties and of reduced color, which derivatives ofcellulose are capable of producing products of greater transparency, bytreating a flowable solution of the derivatives of cellulose withmetals. The treatment may consist in passing the' solution through acolumn containing the metals in a form in which they present a'largesurface area, whereby the solution contacts with a considerable surfaceof metal. However, the metals in a finely divided form may be mixed intothe solution and then filtered out.

While other derivatives of cellulose, such as cellulose nitrate, may betreated in accordance with this invention, we prefer to treat organicderivatives of cellulose, such as organic esters of cellulose andcellulose ethers. ganic esters of cellulose are cellulose acetate, cel-Examples of orderivatives of cellulose, precipitate the organic 7 luloseformate, cellulose 'propionate and cellulose butyrate, while examples ofcellulose ethers are ethyl cellulose, methyl cellulose and benzylcellulose.

The organic derivative of cellulose may. be formed by any suitablemethod. For instance, cellulose acetate may be formed by treatingcellulose with acetic anhydride in the presence of a catalyst andasuitable diluent or solvent such as acetic acid. The cellulose acetatethus formed may be subjected to a hydrolysis or. ripening treatment toproduce the desired solubility characteristics therein. The ripening orhydrolysis may be performed by allowing cellulose acetate, stilldissolved in the liquors formed during esterification, to stand for aperiod of time under suitable temperature conditions. By this processcellulose acetate, which when formed is soluble in chloroform, may bemade soluble in acetone. The other esters of cellulose may be formed ina similar manner. For the purpose of describing this invention and inthe appended claims, the term primary solution refers to a solution ofcellulose ester in the solvent produced or added during theesterification of the cellulose. For instance, the primary solution ofcellulose acetate, formed in accordance with the above describedprocess, is the acetic acid solution of cellulose acetate containingsome sulphuric acid.

Although we have found that satisfactory re- I sults may be obtained bytreating the solutions of v the derivatives of cellulose with a metal ormetals at any time during their manufacture, we prefer to treat thederivatives of cellulose after they have been precipitated from theirprimary solu-' tion, stabilized and dissolved in a second solution,which second solution may be termed for the purpose of this invention, asecondary solution. For instance, we may subject the organic derivativesof cellulose to contact with a large surface of metal or metals whilethe organic derivatives of cellulose are dissolved in their primarysolution and after neutralizing a substantial amount of the catalystemployed in their manufacture.

" The preferred method of carrying out our invention, however, is tofirst neutralize the catalyst present in the primary solution'of theorganic derivatives of cellulose from the primary solution, stabilizethe same by any suitable method and then re-dissolve the organicderivatives of cellulose in any suitable solvent before subjecting theorganic derivatives of cellulose to contact with the metal.

The solution of organic derivatives of cellulose at the time oftreatment with metals may be of any suitable concentration. However, aneasily flowable solution is preferred. For cellulose acetate, a suitableworking solution may consist of from 5 to 25 parts by weight ofcellulose acetate to '75 to 100 parts by weight of acetone. Although anyeasilm flowable solution will give satisfactory results, weprefer -touse a solution containing less than 20 percent of the'organicderivatives of cellulose. The organic derivatives of cellulose may bedissolved in a solvent that is to be employed in forming the sameintqarticles and after treating with the metals the solvent may beremoved to increase the percentage of organic derivatives of celluloseto the proper working conditions.

The treatment with metals is preferably accomplished by passing asolution of the organic derivatives of cellulose through a columncontaining the metals in a form presenting a large surface area.

Although any suitable metal, such as zinc, copper, nickel, cobalt,chromium, lead,

tin, silver, cadmium, iron, aluminum or other metals, may be employedalone or in series, we

prefer to form with two or more metals a voltaic cell or couple. Forinstance, highly satisfactory results have been produced by intimatelymixing copper 'wool, lead wool and iron wool. The metals may be presentin the column in the form of plates, powder, beads, rings, shavings,.curls, turnings, etc. To produce the most eiiicient column metal woolis preferred. The metals, however, may be present in the column in morethan one state. Forinstance, iron wool. may be mixed with copperturningsor the iron may be present both as wool and as shavings mixed withcopper wool and zinc beads. Any suitable mixture of metals may beemployed to form the voltaic cell. The solution may be treated bypassing it through a series of columns each containing a single metal ora single column in which there is a series of layers, each layercontaining The length of treatment may be adjusted by regulating thelength of the column containing the metals, the rate of flow of materialtherethrough or by re-circulating the solution through the columnseveral times. Although the treatment with metals at room temperaturehas been found to be satisfactory, it is preferable to carry out thetreatment at a more elevated temperature. For instance, good results maybe obtained bypassing the solution of organic derivatives of cellulosethrough the column containing metals at any temperature from 15 to 70degrees or more but preferably while maintained at a temperature ofbetween 34 to 41 C.

The passing of the solution of organic derivatives of cellulose throughthe column containing metals may be eflected by gravity or by flowingthe solution through the column under pressure. Whether pressure shouldbe employed depends largely upon the concentration of the derivative ofcellulose solution and the length of time the treatment is desired.

Before or after treating the solution of the de-..

rivative of cellulose with metal, the solution may be filtered throughany. convenient type of the many filter presses or continuous rotatingfilters.

of the solution after treatment with the metals to v remove theinsoluble compounds produced during the treatment. Two or six or morefiltrations may be made through the same or different mesuch as carbonblack, silica, gel, fullers earth or other types of grannular or fibrousmaterial which will aid filtration, or absorb color from the vsolutions. After treatment with the metals, the

' diums. To the solution may be added filter aids constituents which arenot soluble in the solvent may be separated by centrifuging the solutionor by filtering and centrifuging the solution.

The derivative of cellulose, when treated by our process, formsplastics, yarns and the like of greater brilliancy, clarity and freedomof color than may be madeby an untreated cellulose. It is eminentlysuitable for making ,clear plastics that have no pigments or dyes or forthe making of light colored plastics. However, the derivative ofcellulose produced by our process may be employed for makingdark-colored materials.

The derivative of cellulose, when treated by our process, may be formedinto sheets and films by casting the same on film-forming wheels andbelts formed of metal alloys without corroding the same. Films formed ofan untreated derivative of cellulose tend to take on a color or absorbthe discolored products of corrosion from the film casting belt orwheel. This property is obviated from the derivative of celluloseproduced in accordance with our invention and a solution of suchderivatives of cellulose in a volatile solvent therefor may be spun intofilaments through spinning jets made of metal alloys with substantiallyno corrosive action on the spinning jets. Thus, a cellulose derivativeproduced in accordance with our invention forms more uniform filaments,yarns, straws, etc. than those made of untreated derivatives ofcellulose. The spinning into filaments or yarns of an organic derivativeof cellulose, treated in accordance with the present invention, is alsomore economical than the spinning of untreated derivatives of cellulosein that the periods of inspection of the jet orifice may be lessfrequent and the replacing of jets substantially eliminated.

The derivative of cellulose treated in accordance with our invention maybe dissolved withvolatile solvents therefor, and may have incorporatedtherein plasticizers, such as triacetin,

of this invention is in the making of molding powders containing apurified derivative of cellulose in finely divided condition togetherwith plasticizers but containing little or substantially no volatilesolvents, which molding powders may be molded under heat and pressure tothe desired shape. Films to'be employed as a base for photo- Example A10% by weight solution of cellulose acetate in acetone is passed threetimes through a fourfoot pad of a loosely packed mixture of copper wool,lead wool and iron wool. The pressure on The derivatives of cellulosemade in the solution is adjusted such that the flow of cellulose acetatethrough vthe pad requires approximatelyzo minutes. The solution is thenpassed through a filter pad consisting of a six inch layer of wood pulpmaintained in position by a layer of cotton cloth on either side. Theresulting solution isv found to be substantially. free of corrosivematerials and when formed into a film is free of haze and cloudy spots.

The cellulose acetate solution of the above example may be concentrated,by removing a part of the acetone solvent, to a consistency suitable forforming filaments by the dry method of spinning. When formed intofilaments by extruding the same through orifices it produces asubstantially'uniform filament without affecting by corrosion thediameter of the orifice.

It is to be understood that the foregoing detailed description is givenmerely by way of iilustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by LettersPatent is:

Process for improving the properties of substitution derivatives ofcellulose in which the substituent group is organic, which comprisestreating said derivatives of cellulose for at least 5 minutes, while insolution, at a temperature between 34" and 41 C. with a metal in theform of a metal powder, metal wool or similar form presenting a. largesurface area and thereafter separating such solution from the metal.

2. Process for improving the properties of substitution derivatives ofcellulose in which the substituent group is organic, which comprisestreating them for at least 5 minutes, while in solution and at atemperaturebetween 34 and 41 0., with metals in the form of metal wooland thereafter separating such solutions from the metals.

3. Process for improving the properties of cellulose acetate, whichcomprises treating cellulose acetate for at least 20 minutes, whiledissolved in more than five times its weight of a liquid solvent and ata temperature between 34 and 41 C., with a plurality of metals in theform of metal powders, metal wool or similar forms presenting a largesurface area and thereafter separating such solution from the metals.

4. Process for improving the properties of cellulose acetate, whichcomprises treatingcellulose acetate for at least 5 minutes, whiledissolved in more than five times its weight of a liquid solvent and ata temperature between 34 and 41 C., simultaneously with two metals whichform a voltaic couple, each of which is in the form of a between-34 and41 C. with a metal in the form of metalpowder, metal wool or simflarform comprising a large surface area, and thereafter separating thesolution from the metal.

CAMILLE DRE'YI'US. GEORGE SCHNEIDER.

